The invention relates to a sampling head comprising a needle, whose lower end is immersed in a liquid to be sampled and whose upper end is able to pierce a diaphragm sealing a vacuum sampling container, so that a given quantity of liquid is automatically sampled in said container under the suction effect caused by the vacuum prevailing within the container.
In certain industries, such as the chemical and nuclear industries, it may prove necessary to carry out analyses of liquids present in installations. This more particularly applies to certain radioactive liquids in nuclear fuel processing installations.
In order not to disturb the operation of the installation, punctual sampling takes place of the quantities necessary for these analyses. As described in FR-A-1,401,298 and FR-A-2,058,751, a known solution consists of using for this purpose a liquid sampling system having several sampling heads individually connected to different parts of the installation, so as to make it possible to take samples of different radioactive liquids. The sampling system also has a tool system installed in a glove box, which makes it possible to fix a diaphragm sealing the end of a vacuum container to the needle of one of the sampling heads. The latter are then arranged in circular manner to the bottom of a glove box, so that a tool fitted to a rotary plug arranged coaxially to said circle gives access to each of the sampling heads.
In a sampling system of this type, each sampling head comprises a sampling tank fixed in the bottom of the glove box and a removable needle body supporting the needle, which is fitted into a receptacle of the sampling tank. Below the receptacle the needle is immersed in a cavity formed in the sampling tank and at the upper end of which is open to an intake tube and a discharge tube for a fluid to be sampled. These two tubes connect the sampling head to the installation in which the fluid is to be sampled, so that said fluid circulates in the sampling head at least when a sample has to be made on said head. Moreover, a small cross-section passage connects the bottom of the cavity to one of the tubes, in order to permit the emptying or drainage of the cavity when the circulation of the liquid to be sampled in the sampling head is stopped.
In such a sampling head, the drainage passage issuing into the bottom of the cavity helps to create turbulence within the latter. Thus, instead of only sampling the liquid, it frequently occurs that the containers suck in a large amount of gas, so that the liquid quantity sampled in the container proves inadequate for the analyses to be carried out. However, it is not possible to avoid the existence of the draining passage, because the need to drain the cavity every so often is vital for the quality of the samples taken.